Storm Season Begins Wednesday

We will enter a much stormier pattern Wednesday that will persist through the weekend and possibly beyond, with moderate/strong systems affecting the area every 24-36 hours. Because these storms will be quick-moving and temperatures will be relatively cool, no flooding is expected and we will instead see significant early-season snowfall in the mountains. Not enough to open the resorts, but enough for those willing to hike to get some turns in!

California Wildfires

Before I delve too deeply into the storms slated for this week, I want to touch on the wildfires that initiated last week over California. One of the great paradoxes of autumn weather in the West is how a deep, cold upper-level trough over the Intermountain West – like the one we saw last week that caused Denver to drop 70 degrees in 18 hours – can cause extreme fire danger over parts of California. Because cold air is more dense than warm air, these upper-level-troughs are often associated with surface high pressure, and with relatively lower pressure over California, extremely strong offshore gradients form. These offshore gradients drive downslope winds that bring this cold, dry, high-elevation air over the Great Basin to sea-level, warming it substantially via adiabatic compression in the process. The combination of extraordinarily dry air, fierce winds, and warm temperatures create the conditions necessary for rapid fire growth.

These wind events – known as Diablo winds in Northern California and Santa Ana winds for Southern California – have caused tremendous amounts of damage in recent years, particularly for Northern California. The 2017 North Bay Fires and 2018 Camp Fire caused over 30 billion dollars of damage and 129 fatalities in total, and there were many other damaging and deadly fires besides these over the past two years throughout the state. I wrote a post all about Diablo/Santa Ana winds (with the Camp Fire as a case study) last year, give it a read if you feel so inclined.

Amazingly, Northern California saw no major fires or fatalities from this most recent Diablo wind event. The reason? PG&E (Pacific Gas & Electric, a utility covering much of Northern and Central California) took extreme precautionary measures and shut off power to 738,000 customers. Power has since been restored to all customers. Downed live electrical lines are a common source of fire starts, and the Camp Fire was caused by a downed, live PG&E transmission line.

While this can’t have been fun for those who lost power, this was absolutely the right decision by PG&E. There was extensive damage to the electrical grid, and we would have seen a catastrophic event if they did not take these extreme measures.  Well done PG&E!

Going back to our discussion of the change to a much stormier pattern slated for Wednesday, I would be remiss if I didn’t mention the role that Typhoon Hagibis – a very large, Category 2 typhoon that hit Tokyo (previously a Category 5 over the West Pacific)  before becoming entrained into the westerlies – played in our shift to a rainier pattern. The remnants of typhoons can feed some truly exceptional extratropical storms – in fact, another Typhoon Hagibis (2007) fed the Great Coastal Gale, which was the Northern OR/Southern WA Coast’s strongest storm on record. 2019’s Hagibis won’t spawn any particularly noteworthy storms, but it will provide enough extra “juice” to make this week the wettest and windiest one since last winter.

Super Typhoon Hagibis’ week-long journey to Japan. pic.twitter.com/tZblsp9EVm

— Dakota Smith (@weatherdak) October 13, 2019

This animation was created by Dakota Smith – a fellow science geek and great all-around guy. Follow him on Twitter and Facebook for cool science insights and absolutely spectacular satellite imagery, subscribe to “Okay Let’s Science,” his Youtube Channel dedicated to all things science, and definitely check out his awesome Weather Junkies podcast that he runs with WPTZ meteorologist Tyler Jankowski (and listen to the podcast I was featured on here!)

The Storms This Week

As mentioned above, none of the storms we’ll see this week will be particularly memorable, but they’ll still be strong enough to significantly impact your day. Let’s go through them in order.

Storm #1:  Tuesday night/Wednesday

Our first storm is currently visible as that huge, tropically-fed cyclone spinning in the Gulf of Alaska. However, if you look a little bit further east towards the 140⁰ W longitude line, you’ll see that there’s a pretty substantial ridge ahead of this cyclone. This ridge will move over us on Monday and will slowly move inland on Tuesday, allowing this storm’s cold front to slowly move inland. The Olympic Peninsula should begin to see rain by Tuesday morning, but precipitation should hold off for the Portland metro area until Tuesday night, and by this time, the front will have weakened significantly anyway.

But this front will have accomplished the arduous task of punching through an upper-level ridge, which is never an easy obstacle to surmount. Another front will follow right on its heels Wednesday afternoon and bring steady precipitation through Wednesday evening.

To put this in football terms, think of Monday’s ridge as a big, fat defensive nose tackle, Tuesday’s front as a fullback laying down a mean lead block, and Wednesday’s front as a running back taking advantage of the open lane. In fact, this front/running back is expected to break into the secondary and make it into Western Wyoming before he encounters the Tetons (this isn’t your typical gridiron) and stumbles.

Storm #2: Thursday and Friday

Another quick-moving cold front will push through the area on Thursday, with widespread showers Friday and decreasing showers Saturday. We’ll have strong onshore flow and well-below average temperatures (highs in the mid 50s Friday and Saturday for PDX), and both of these will allow snow to pile up in the mountains. The UW WRF shows 1-2 feet above 5,000 feet and even has some snow reaching all the way down to Snoqualmie Pass and Government Camp on Saturday morning. The really heavy stuff will be over the higher terrain of the BC Coast Range, where multiple feet of snow are expected.

Storm #3: Sunday

By Sunday, a ridge will begin to build in the Eastern Pacific, but another moderate/strong system is expected to slide into the Pacific Northwest. This system is expected to bring another bout of heavy rain, mountain snow, and gusty winds along the coast, but with ridging taking hold it should have relatively little shower activity in its wake.

Total Precipitation

The UW WRF models shows some spots along the Coast Range, Olympics, and Cascades picking up 5-10 inches over the next week, with 1-3 inches likely in the Western WA/OR lowlands. Because these series of storms are relatively cool and the rivers are running low, flooding is not expected, but river levels will definitely rise.

High Waves Offshore

With strong, persistent westerly flow, we’ll also see some massive waves offshore this week despite the fact that none of these storms will have particularly noteworthy winds themselves. If you were pondering a deep-sea-fishing trip this week (they are still catching tuna out there!), I’d recommend fishing one of our wonderful area lakes instead.

Atmospheric River Next Week?

As mentioned above, the storms we’ll see this week are relatively cool and the mountains above 5,000 feet will see gobs of snow. However, there is the potential for flooding at the beginning of next week – but only if the ridge that models currently show is significantly weaker than currently modeled. These models have been consistent in showing a strong atmospheric river impacting Central British Columbia but currently keep the Pacific Northwest mostly dry. If future runs bring this atmospheric river further to the south, we could be talking about our first flood event of the season.

Our opening salvo of autumn storms is always one of my favorite weeks of the year. I hope you’ll enjoy the storms as much as I will!

Charlie